It's official: Windows Blue is Windows 8.1

We expected as much, and today Microsoft has removed all doubt: the Windows Blue update we've been banging on about lately will officially go by the name of Windows 8.1 when it's released later this year.

The update, which will be rolled out as a free update, will cover both Windows 8 and the ARM-centric Windows RT, though whether it will draw the two closer together remains to be seen.

Some have claimed recently that Blue will effectively see Windows RT scrapped altogether and absorbed under the wider Windows 8 umbrella.

Microsoft's latest comments, which come from Windows CMO and CFO Tami Reller, don't specifically rule that out, but make no mention of it either. We'd also previously heard that Blue was the codename for a full spectrum of Microsoft OS updates, including Windows Phone 8, but Reller's comments don't refer to the smartphone OS at all.

What she did say is that Windows 8.1 will be free of charge, and available from the home screen when it does launch. As for when that'll actually be, she wasn't saying, mentioning only that it'll be released “later in the calendar year” and that “we know when the holidays are”.

In the more immediate future, a preview version will be made available on June 26 at the start of Microsoft's Build 2013 developer event.